The overall objective of this proposal is to identify the molecular determinants that are involved in the subtype-selective binding of the hallucinogenic drug, salvinorin A, to the kappa opioid receptor (KOR). The molecular determinants involved in the selective binding of salvinorin A to KOR will be examined using opioid receptor chimeras and KOR mutants. Initial studies using KOR/DOR chimeras have demonstrated that TM2 of KOR is critical for the subtype-selective binding of salvinorin A. Site-directed mutations will be introduced at non-conserved amino acids in TM2 of KOR with the cognate amino acids in DOR to identify residues that are involved in salvinorin A binding. The ability of these KOR mutants to increase ERK1/2 phosphorylation and inhibit adenylyl cyclase activity will also be examined. Additional radioligand binding studies will use a series of genetically engineered KOR/MOR chimeras to identify transmembrane segments that permit selective binding of salvinorin A and 2-salvinorinyl benzoate to KOR and MOR, respectively. Understanding the molecular basis for the selectivity of salvinorin A-KOR interactions will provide insight for the rational design of salvinorin A analogs that could potentially represent novel therapeutic agents. [unreadable] [unreadable] [unreadable]